#include <iostream>
#include <string>
using namespace std;

int main(){
   string a,b;
   cin >> a >> b;
   if(a.size() > b.size()){
      cout << a << endl;
      return 0;
   }else if(a.size() < b.size()){
      cout << b << endl;
      return 0;
   }else{
      for(int i = 0;i < a.size();i++){
         if(a[i] == b[i]) continue;
         else if(a[i] == '4' && b[i] == '7'){
            cout << a << endl;
            return 0;
         }else if(a[i] == '7' && b[i] == '4'){
            cout << b << endl;
            return 0;
         }
         if(a[i] > b[i]){
            cout << a << endl;
            return 0;
         }else if(a[i] != b[i]){
            cout << b << endl;
            return 0;
         }
      }
   }
}